#!/usr/bin/env perl

use strict;
use warnings;
use Getopt::Std;

my @patterns = (
    qr/error/i,
    qr/FATAL/,
    qr/Critical/,
    qr/exception/,
);
my $re = join '|', @patterns;

my %opt = ( B => 5, A => 5 );
getopts('B:A:', \%opt);

my $window = $opt{B} + $opt{A} + 1;
my $emit = 0;
my @lines;

while (<>) {
    $emit = $window if /$re/;
    splice(@lines, 0, 0, $_);
    --$emit < 0 ? splice(@lines, $opt{B}) : print splice(@lines, -1);
}